High-frequency transfer of cloned herpes simplex virus type 1 sequences to mammalian cells by protoplast fusion

Stable induction of a 51K cellular protein in neuronal cells surviving herpes simplex virus type 1 infection

A series of survivor cell lines derived by infection of B103 rat neuroma cells with active wild-type herpes simplex virus type 1 (HSV-1) (M. Levine, A. L. Goldin, and J. C. Glorioso, J. Virol. 35, 203-210 (1980)) has been isolated. The survivor cells produced no infectious virus, yet they continued to react with HSV-1 antiserum for over 100 cell generations following the initial infection. The reactivity of the survivor cells with HSV-1 antiserum is characterized as being due to expression of a 51K protein. The 51K protein reacted with antiserum prepared against HSV-1 virions and was not detectable in the parental B103 cells. A protein of the same molecular weight was seen in productively infected B103 and HEL cells. The protein detected in the survivor cells comigrated with that seen in the infected cells on two-dimensional gel electrophoresis, indicating that they represent similar proteins. Despite the presence of the 51K protein reactive with HSV-1 antiserum, the survivor cells contain no detectable HSV-1 DNA sequences. They do contain DNA sequences which cross-hybridize with HSV-1 DNA, but similar cross-hybridizing sequences were also present in the parental B103 cells. No hybridizing polysomal, polyadenylated RNA species were present in the survivor cells that were not present in the parental B103 cells when probed with the cross-hybridizing HSV-1 restriction fragments. Therefore, the 51K protein evidently represents a cellular protein induced by the HSV-1 infection.

Effect of cell cycle position on transformation by microinjection

We have investigated the effect of cell cycle position on the efficiency of transformation by microinjection. Linear recombinant plasmids transform synchronized cells with similar frequencies following injections at all cell cycle stages, whereas supercoiled molecules show a decreased ability to generate transformants in early S phase. This inhibition is not due to an inability to transiently express a transferred gene, since cells at all stages of the cycle efficiently expressed a hamster adenine phosphoribosyltransferase gene introduced on a supercoiled plasmid. Southern transfer analyses of the cell cycle specific transformants revealed that tandem arrays of plasmids, integrated into the host chromosomes, could be generated at all cell cycle stages.

A cloned human immunoglobulin heavy chain gene with a novel direct-repeat sequence in 5' flanking region

A rearranged human immunoglobulin gamma 1 heavy-chain gene (HIG1) was cloned from a human plasma cell leukemia cell line, ARH-77. The cloned gene possessed a unique direct repeat sequence of 84 bp in the 5' flanking region as well as an enhancer-like element in the JH-C gamma 1 intron. The latter sequence is located 1 kb downstream of 3' end of the J6 exon. The direct-repeat sequence in the 5'-flanking region contained a core-like sequence resembling that of viral enhancer elements. It is located in the intron between two leader exons. P1 nuclease mapping and exonuclease VII digestion experiments showed that most of the direct repeats are noncoding regions and spliced out from the transcript. These data suggested that HIG1 gene might have two kinds of enhancer-like elements at both sides of the V region gene. HIG1 gene has been introduced by the protoplast fusion into mouse myeloma cells (NSI and J558L cells) and mouse fibroblasts. A pSV2gpt vector containing HIG1 gene (pSV2-HIG1) was used to transform the cells. The amounts of mRNA synthesized in the transformed cells were at least 50 to 100 times larger than those in ARH-77 cells, although about one copy of HIG1 gene was present in DNA of a transformed cell. HIG1 gene was not expressed in fibroblasts, indicating that the enhancer of HIG1 gene acts in a tissue-specific manner but not in a species-specific one. The role of two kinds of enhancer-like elements in HIG1 gene is discussed in connection with the high-level expression of this gene in mouse myeloma cells.

Production of functional chimaeric mouse/human antibody

The availability of monoclonal antibodies has revived interest in immunotherapy. The ability to influence an individual's immune state by administering immunoglobulin of the appropriate specificity may provide a powerful approach to disease control and prevention. Compared with immunoglobulin from other species, human immunoglobulin (Ig) might be best for such therapeutic intervention; it might function better with the recipient's effector cells and should itself be less immunogenic. The success of the mouse hybridoma system suggests that immunoglobulin of virtually any specificity can be obtained from a properly immunized animal. In the human system, however, immunization protocols are restricted by ethical considerations, and it is not yet clear whether human antibody-producing cell lines of the required specificity can be obtained from adventitiously immunized individuals or from in vitro immunized cells. A method which might circumvent these difficulties is to produce antibodies consisting of mouse variable regions joined to human constant regions. Therefore, we have constructed immunoglobulin genes in which the DNA segments encoding mouse variable regions specific for the hapten trinitrophenyl (TNP) are joined to segments encoding human mu and kappa constant regions. These 'chimaeric' genes are expressed as functional TNP-binding chimaeric IgM. We report here some of the properties of this novel IgM.

Human alpha- and beta-globin gene transcription in mouse erythroleukaemia cells

Human beta-globin genes introduced into mouse erythroleukaemia (MEL) cells by DNA co-transformation are correctly regulated when erythroid cell differentiation is induced by dimethylsulphoxide (DMSO). In contrast, cloned human alpha-globin genes are efficiently transcribed in MEL cells before induction, and no increase in the level alpha-globin mRNA is observed when the cells differentiate. These observations suggest that the mechanisms by which alpha- and beta-globin genes are activated during erythroid cell differentiation are fundamentally different. Analysis of the transcription of hybrid human alpha-beta-globin genes in MEL cells revealed that the sequences responsible for differences in transcription of the intact alpha- and beta-globin genes are located on the 3' side of the mRNA capping site of the two genes, suggesting that cis-acting regulatory sequences are located within the structural genes.

Differences in human alpha- and beta-globin gene expression in mouse erythroleukemia cells: the role of intragenic sequences

Human beta-globin genes introduced into mouse erythroleukemia (MEL) cells by DNA cotransformation are correctly regulated when erythroid cell differentiation is induced by dimethylsulfoxide (DMSO). In contrast, cloned human alpha-globin genes are efficiently transcribed in MEL cells prior to induction, and no increase in the level of alpha-globin mRNA is observed when the cells differentiate. These observations suggest that the mechanisms by which alpha- and beta-globin genes are activated during erythroid cell differentiation are fundamentally different. Analysis of the transcription of hybrid human alpha/beta-globin genes in MEL cells revealed that the sequences responsible for differences in transcription of the intact alpha- and beta-globin genes are located on the 3' side of the mRNA capping site of the two genes, suggesting that cis-acting regulatory sequences are located within the structural genes.

Somatic cell hybrid selection with a transfectable dominant marker

A recombinant plasmid vector, pSV2-neo, coding for resistance to neomycin and the related antibiotic G-418, was transfected into the mouse myeloma line X63-Ag8.653 by a modification of the protoplast fusion technique. The time interval required to obtain 10(6) G-418 resistant cells was 20 days and the efficiency was 10(-4)-10(-5), which represents a significant advantage over classical methods of selecting mutant cells bearing a dominant selection marker. To investigate the efficiency of this marker in somatic cell hybrid selection, these cells were fused to the human myeloma line U-266 and the hybrids were selected either in HAT + G-418 or HAT + ouabain. The pSV2-neo vector was as efficient as ouabain as a dominant marker with respect to the number of viable hybrid colonies selected and their levels of immunoglobulin secretion. The reciprocal experiment was also performed: HAT-sensitive, mutant U-266 cells were transfected with pSV2-neo, clones selected in G-418 and fused with X63-Ag8.653 cells, and hybrids selected in ouabain plus G-418, yielding HAT-sensitive hybrid "heteromyelomas" that were effective fusion partners with human B lymphocytes.

Herpes simplex virus thymidine kinase gene is stably maintained and expressed in cells transformed by protoplast fusion

We examined a series of transformed cell lines resulting from transfer of the herpes simplex virus type 1 thymidine kinase gene to Ltk- cells by protoplast fusion gene transfer. We show that multiple copies of the transforming plasmid DNA, ranging from a minimum of two to greater than 20, were present in one or at most a few integration sites in each cell line. The TK+ phenotype was stable in five independent transformed cell lines after growth in nonselective medium for over a year. Transforming plasmid DNA was stable in one cell line containing from two to five copies after a year of growth in nonselective medium. In another cell line initially containing about 20 copies, the transforming DNA became rearranged soon after growth to mass culture, resulting in a decrease to two to five copies which then remained stably maintained. This suggests that TK+ transformants resulting from protoplast fusion are stable when the input DNA has integrated in a relatively low copy number.

Activation of a translocated human c-myc gene by an enhancer in the immunoglobulin heavy-chain locus

A tissue-specific transcriptional enhancer element that is associated with the human immunoglobulin heavy-chain locus is defined. In a non-Hodgkin's lymphoma that contains a translocated c-myc gene this enhancer is retained on the 14q+ chromosome and occurs within sequences shown to activate previously cryptic promoters of the c-myc gene.

Introduction of purified genes into mammalian cells

There are a number of methods to introduce genes into mammalian cells. These include cell hybridization, chromosome-mediated and DNA-mediated gene transfer. DNA-mediated transfer can be achieved by direct microinjection methods or by indirect methods. The DNA enters the nucleus and is expressed in a high proportion of cells transiently. The DNA then becomes integrated into host cell DNA at random sites resulting in more stably expressing transformants. A number of genes for which selection systems exist can be introduced into mammalian cells. Nonselectable genes can also be introduced into cells by either ligating them to a selectable gene or by mixing them with carrier DNA and a selectable gene. If an amplifiable gene sequence is introduced into cells, it and other genes in its proximity can be coamplified. Amplification of the genes can also be achieved by the use of appropriate viral vectors and recipient cells. The foreign genes are expressed in the recipient cells if they contain the appropriate recognition signals for initiation and termination of transcription. Transfection systems are thus permitting identification of DNA sequences which have a regulatory role in gene expression. The identification of transcriptional signal sequences has formed the basis for construction of appropriate molecules which would permit expression of genes which cannot normally be expressed in mammalian cells (e.g., bacterial genes). The foreign genes are not only expressed in the recipient cells but they can also be subject to regulation in the appropriate environment. This observation is paving the way for identification of regulatory sequences. The foreign DNA sequences integrated into the host genome can be recovered by a variety of methods. Such methods permit isolation of genes which code for a selectable gene product.

Analysis of CAD Gene Amplification Using a Combined Approach of Molecular Genetics and Cytogenetics

CAD is a multifunctional protein which catalyzes the first three steps of de novo uridine biosynthesis. Rodent cells resistant to PALA, a specific inhibitor of the ATCase activity of CAD, overproduce the CAD protein and CAD mRNA as a direct result of the amplification of the CAD gene. In order to study the mechanism of CAD gene amplification, a functional Syrian hamster CAD gene was inserted into a cosmid vector using molecular cloning techniques. The cloned genes were assayed for biological function by fusing CAD-deficient Chinese hamster ovary (CHO) cell mutants with protoplasts of E. coli containing the CAD cosmids. Two clones with functional CAD genes were isolated and shown to contain inserts 40 and 45 kb long. The cloned genes could also be introduced into wild type CHO cells by selecting for cells which became resistant to high PALA concentrations in a single step. Transformations of mutant and wild type CHO cells contained multiple active copies of the donated Syrian hamster CAD genes in addition to their endogenous CHO CAD genes. The cloned genes in all transformants analyzed are integrated into host cell chromosomes at single locations defined by in situ hybridization. Independently isolated transformants contain the donated genes in different chromosomes. Co-transformation of CHO cells with two different genes by protoplast fusion is also shown to be possible.

Functional expression of a transfected murine class II MHC gene

The activation of T helper lymphocytes involves the recognition of class II major histocompatibility complex antigens, which are dimeric glycoproteins (of subunit composition A alpha A beta or E alpha E beta) expressed on the surfaces of macrophages and B lymphocytes. One approach to understanding the relationship between the structure of these antigens and their functions in the immune response is to clone the genes that encode them, to obtain functional expression of the cloned genes transfected into an appropriate cell line, and then to see how those functions are affected in variant genes generated in vitro. We report here the expression in Iad-bearing B cells of an Ak beta gene, which confers on the transfected cells the capacity for both allostimulation and antigen-dependent activation of an I-Ak-restricted T-cell clone.

Analysis of gene expression using simian virus 40 vectors

Extensive studies on the DNA tumor virus Simian Virus 40 (SV40) have provided a wealth of information regarding the genome organization, regulation of viral gene expression, and the mechanism of DNA replication. SV40 can grow lytically in permissive monkey cells or the viral DNA can integrate into the host genome of nonpermissive rodent cells causing morphological transformation. The viral DNA exists as a minichromosome within the nuclei of lytically infected cells and, as a consequence of DNA replication, there is a significant amplification of the viral genome during infection. These properties suggested that SV40 could be developed as a transducing vector to introduce exogenous DNA into mammalian cells and to express this foreign DNA during the SV40 infectious cycle. In this article the properties of SV40 virus vectors and SV40 hybrid plasmid vectors are described and contrasted.

Interferon inhibits transformation of mouse cells by exogenous cellular or viral genes

Specific genes can be introduced into cultured mammalian cells by DNA transfer, sometimes to be stably integrated and expressed. Because interferon inhibits the transformation initiated by DNA viruses, we wondered if it might also affect transformation induced by recombinant plasmids and cellular genes. We show here that in mouse L cells interferon treatment prevents stable integration and expression of the transfected plasmids containing the cloned herpesvirus thymidine kinase (tk) gene, or the dihydrofolate reductase (dhfr) gene from hamster ovary cells. In contrast, interferon does not prevent transient expression of the tk gene in unintegrated form.

Transfer of a cloned immunoglobulin light-chain gene to mutant hybridoma cells restores specific antibody production

The expression of immunoglobulin (Ig) genes is regulated at several levels. For example, although kappa-chain production requires a DNA rearrangement that juxtaposes variable and joining segments, this rearrangement is not sufficient for kappa-chain gene expression; that is, some cell types do not permit immunoglobulin production. The mechanisms responsible for the regulation of the expression of rearranged immunoglobulin genes are poorly understood. The technique of modifying cloned genes in vitro and transferring the modified genes to cells in culture provides a tool for identifying the structural features required for gene expression. To analyse immunoglobulin genes in this manner, however, it is first necessary to use, as recipients, cells that normally permit immunoglobulin production. We report here that a cloned kappa-chain gene is expressed in immunoglobulin-producing hybridoma cells. Furthermore, the product of the transferred kappa-chain gene is capable of restoring specific antibody production to the transformed cells.

Introduction of Escherichia coli cells and spheroplasts into Vinca protoplasts

In the presence of 10% polyvinyl alcohol (PVA), Escherichia coli cells or spheroplasts can be easily introduced into Vinca protoplasts by endocytosis. Uptake proceeded quite rapidly; bacterial cells or spheroplasts were found within the cytoplasm of Vinca protoplasts after 10 min of incubation with PVA.

High-efficiency transfer of DNA into eukaryotic cells by protoplast fusion

Protoplast fusion is a highly efficient method for effecting gene transfer to cells in culture resulting in stable transformation at high frequency. A number of cell lines have been used successfully as recipients. There is no need to isolate and purify the DNA, which not only saves time and effort but eliminates steps that cause nicking or breaking of large cloned inserts. The high-frequency transformation achievable by protoplast fusion should make this procedure useful for studies on gene expression and for screening cloned genomic libraries for genes that can be expressed in recipient cells.